I have taken a cold backup of my RAC database. After that my standby database is not in sync. And noticed that the archive generation sequence of thread 3 was changed from 8209 to 8214. Which makes my standby not in sync. Please find the archive generation.. from the below alert log. Now, the question arises in my mind. How the sequence was changed. And how to bring my DR standby database in sync together.

view the alert.log and identify messages that occurred between the timestamps for the two :

Thread 3 advanced to log sequence 8209 (LGWR switch)

Thread 3 advanced to log sequence 8214 (LGWR switch)

Was there a database shutdown and restart ? Was the database archivelog mode switched to NOARCHIVELOG and back to ARCHIVELOG ? Is the database running in FORCE_LOGGING mode ? (Query V$DATABASE for ARCHIVELOG mode and FORCE_LOGGING mode)

The database was shutdown during the time to take the cold backup for the database. And then started again. We haven't changed any thing coming to the archive mode. It is always archive before and after.